Matt Keller spent a decade in Washington lobbying senators and congressmen on campaign finance reform and ethics legislation. But lobbying the Pope presented a unique challenge to the 42-year-old former senior staffer at Common Cause, who could once get John McCain or Warren Beatty on the phone. Keller has, since 2003, worked for the United Nations World Food Program in Rome, and his mission, ahead of the Pope's trip to Brazil, was simple: get Benedict XVI to mention the aid group's annual worldwide anti-hunger march, Walk the World, which coincided with the final day of the pontiff's trip. And Benedict could be assumed to be amenable: After all, he has repeatedly called for action against hunger, and even commended last year's Walk the World march during a weekly prayer in Rome. Still, a papal endorsement amid the raised visibility of the Brazil trip would be both a bigger boost and a bigger challenge, given the clamor of demands on the papal agenda while he's abroad.

Getting access to the Pope proved incomparably more difficult than lobbying Washington lawmakers. "Talking to someone like me is part of certain people's job description [on Capitol Hill]," says Keller. "At the Vatican, it all seems so shrouded in mystery." But as an advocate for the global poor, his objective is not crafting legislation, but "raising visibility." And on that front, Keller quips, "The Pope is a 2-for-1 deal. He's world famous, and can speak with moral authority."

Keller began in March by helping draft a letter addressed to the Pope from the U.N. agency, asking him to again announce his support for Walk the World. But he knew that in order to achieve his goal, he had to find someone who both shared his agenda and also had direct access to the pontiff.

After querying cardinals, church aid groups and Brazilian officials, in late April Keller was told by a Brazilian diplomat that his best bet might be Rev. Martinho Lenz, the former rector of the Brazilian seminary in Rome and a longtime advocate for the poor who was now working on the agenda for the conference of Latin American bishops to be attended by the Pope.

After a brief but intense email correspondence with Lenz, Keller made one last push, just 36 hours before the Pope headed for Sao Paulo. He went in person to Duncan MacLaren, executive director of the worldwide Catholic charity Caritas, at the group's Vatican headquarters. Keller asked MacLaren to contact Father Lenz. "My contacts at the foreign ministry say he's the person in Brazil that can make this happen. What do you think about your calling him with me here? The more times he hears about this, the better."

But they were unable to get Lenz on speakerphone, and drafted a joint email instead. Said the Scottish-born MacLaren, who's been in Rome for 14 years: "It's a long process. You can't just ring up the Pope. You have to use your natural contacts in the [Vatican bureaucracy]. It's Italian culture here too  who you know is important."

By the Pope's second day in Brazil  with Keller in Sao Paulo monitoring his every word and simultaneously working with a local group to organize thousands to join the march on May 13  an email arrived from Lenz: the Pope's top aides had been made aware of the hunger event. On May 12, the Pope's final evening in Brazil, Keller got an email that left him elated. Lenz had been told that the Pope would indeed mention the march the following day during a speech to hundreds of thousands of Brazilians.

Back in Rome, Keller tallies the results of his unique lobbying adventure. The Pope, speaking on Sunday in Portuguese, had indeed cited his support for the World Food Program's march, which had prompted several Catholic publications to publish stories about it. Ironically, though, the endorsement didn't make it into the coverage of Reuters and the Associated Press, being drowned out by the larger themes of the Brazil trip. In fact, the WFP had gotten better wire-service coverage for Benedict's backing of their march last year, during a prayer service in Rome. Undeterred, Keller's mind is already at work on a strategy to get an even stronger blessing from the Pope. "Next year," the lobbyist says, "we want him to walk with us."